1. Field of the Invention
This invention relates to circuit breakers and, more particularly, it pertains to a contact operating structure with an improved adjustable withstand and current limiting of short circuit current.
2. Description of the Prior Art
Prior art low voltage, power class circuit breakers have been used with movable contact structures and operating mechanisms for providing protection for electrical circuits against electrical faults, and more particularly, electrical overload conditions, low level short circuit or fault current conditions, and, in some places, high level short circuit or fault current conditions. Such prior art devices have utilized a trip mechanism for controlling the movement of an overcurrent toggle structure for separating a pair of electrical contacts upon the occurrence of an overload condition or upon a short circuit or fault current condition. These trip mechanisms have also included a bi-metal movable in response to an overload condition to rotate a trip bar to open a pair of electrical circuit breaker contacts. Moreover, the trip devices have utilized a magnet-driven or electromagnetic-driven armature movable in response to the flow of short circuit or fault current to similarly rotate the trip bar to cause the pair of contacts to separate.
While large amounts of current and/or voltage are involved, a primary circuit breaker is provided with a plurality of secondary breakers downstream leading to specific current loads. Where a specific load generates an overcurrent condition which is handled by a particular secondary circuit breaker, the primary breaker is also involved. However, it is usually undesirable to actuate the primary breaker and thereby interrupt current through the several other secondary breakers to their respective loads. For this reason, it is desirable to delay actuation of the primary breaker and withstand the short circuit current until the secondary breaker has an opportunity to trip. The device at the present level of the fault current, the primary breaker will be tripped, its contacts parting rapidly, and fault current limitation is achieved of the present invention involves and satisfies this particular circumstance.